1. Field of the Invention
The present invention relates to surgical devices and methods for repairing orthopedic injuries, and, more particularly, to devices and methods for repairing soft-tissue tears and for affixing soft tissue to bone.
2. Description of Related Art
The repair of soft tissue tears represents a persistent problem in orthopedic practice. It is known to apply sutures and various types of fixation devices to such tears. The fixation of soft tissue to a bone, and that of bone pieces to each other, is an additional frequently encountered problem. A related condition, osteochondritis dissecans (OCD), results in the splitting of pieces of cartilage into a joint, such as a knee joint or shoulder joint.
Sutures, barbs, and various types of screws are known to be used to bring two sides of a tear into apposition; screws are also known for use in fixing two sections of bone together and for fixing a piece of soft tissue to bone. A number of fastener-type devices are known in the art: Screiber (U.S. Pat. No. 4,873,976); Bays et al. (U.S. Pat. Nos. 4,884,572 and 4,895,148); Winters (U.S. Pat. No. 5,059,206); and Justin and Winters (U.S. Pat. Nos. 5,503,634 and 5,730,744). Bone screws are disclosed by Huebner et al. (U.S. Pat. Nos. 5,562,672, 5,871,486, and 5,964,768).
It is an object of the present invention to provide a screw, delivery device, and method for repairing an orthopedic injury.
It is a further object to provide such a screw that is made from a nontoxic, biocompatible, bioabsorbable plastic specially designed to maintain its structural integrity during the healing of the tear and to prevent tissue abrasion.
It is an additional object to provide such a screw having a shape designed to compress a tear and to pull soft tissue onto a bone.
It is another object to provide such a screw shaped to resist forces tending to pull apart a tear during healing or to pull soft tissue away from a bone.
It is also an object to provide such a screw that resists stripping and has superior tissue retention characteristics.
These and other objects are attained with the screw and delivery device system and method of the present invention, an orthopedic screw for repairing a tear in soft tissue of a patient, for affixing soft tissue to a bone, and for affixing a condyle to a bone surface. The fastener has a head at a proximal end and a root extending between the head and a distal end. A distal section of the root has a narrowing cross section toward the distal end. In use an insertion of the fastener into soft tissue is facilitated by this narrowed distal end, which takes the form in a preferred embodiment of a generally conical-shaped distal tip as a lead-in geometry of the root.
The fastener further has a helical thread, a protrusion that extends along at least a portion of the root. A leading end of the thread begins at a location in spaced relation from the distal end, and a trailing end of the thread meets the head at the root""s proximal end. Along a leading section the thread extends from the leading end and has a substantially constant helical pitch; along a trailing section between the distal section and the trailing end, the thread has a helical pitch that decreases in a proximal direction, so that the pitch adjacent the head is smaller than that along the distal section. In use the decrease in the helical pitch along the trailing section serves to bring two pieces of tissue into apposition as the screw is advanced across the two pieces of tissue in a screwing motion. The substantially constant pitch along the leading section assists in preventing a stripping of the thread, which is more likely to occur with a screw having a variable pitch along a leading section.
At the proximal end the head has a diameter greater than a major root diameter of the proximal section. The head is for improving the tissue retention characteristics of the screw.
In an alternate embodiment, the thread also has means for resisting an axial force from pulling the screw out of the tissue and from pulling the two pieces of tissue apart. Specifically, the resisting means comprises the thread having a buttress form.
In a preferred embodiment, the screw material comprises a biodegradable plastic biocompatible with the soft tissue of the patient. The material is specifically designed to be biodegradable within a first time span greater than or equal to a second time span over which the two pieces of tissue can knit together. This feature permits the fastener to remain in place for as long as required for the tissue to heal, but ultimately to biodegrade and be dissipated harmlessly into the patient""s system. Alternatively, the material in some procedures may be desired to be nonbiodegradable and remain in place permanently or until surgical removal.
The material is further preferably designed to have elastomeric properties compliant with those of the tissue to be repaired in order to confer biofunctionality.
A further feature of the present invention comprises a delivery device for introducing the above-described screw into the area of the patient""s tissue to be repaired. A feature of the screw permitting a mating with a delivery device comprises the screw""s having an axial bore extending along the helical axis proceeding from the proximal end. The bore preferably has a noncircular cross-sectional shape so that an elongated driving device having a noncircular cross-sectional shape and dimensioned to pass into the bore can enter the bore and turn the screw. The screw can then be advanced into the target tissue by being rotated by the driving device in a direction having a handedness commensurate with the thread. Simply put, the screw is internally drivable by rotation of an elongated member inserted into its bore, which then also supports the screw by imparting additional rigidity during the driving procedure. This is a desired feature if the screw material is flexible.
The elongated driving device of the present invention for driving the screw as described above has a distal end having means for mating with the screw""s proximal end, and a proximal end having means for being rotationally driven. In use the screw is mated with the driving device""s distal end, the screw and distal end of the driving device are positioned adjacent the first piece of tissue, and the means for being driven is rotated in a direction having a handedness commensurate with the thread, thereby advancing the screw into the tissue pieces until the separation therebetween is breached.
In a specific embodiment of the system, the driving device further has a noncircular cross-sectional shape along a distal section adjacent the distal end. The screw""s bore as described above has a noncircular cross-sectional shape dimensioned to permit the distal section of the driving device to pass into the bore and to permit relative axial sliding and rotational coupling movement therebetween. The axial slidability permits the driving device to be mated by sliding the driving device distal section into the fastener bore and to be removed once the tissue pieces have been joined together by sliding the driving device out of the bore.
The method of the present invention is for repairing an orthopedic tissue injury in a patient. The method comprises the steps of providing a screw having the features as described above. The screw is then inserted into an area adjacent the first piece of tissue. The distal end of the screw is manipulated to a desired position. In the case of a tear, the desired position is generally normal to a long axis of the tear, and the screw is driven across the tear in a screwing motion. The decrease in the helical pitch serves to bring two sides of the tear into apposition as the screw is advanced. In the case of attaching and/or drawing two pieces of tissue together, the desired position is through one piece of tissue and adjacent the second piece. The screw is driven through the first piece of tissue and into the second, with the decrease in helical pitch bringing the two pieces of tissue together.
The features that characterize the invention, both as to organization and method of operation, together with further objects and advantages thereof, will be better understood from the following description used in conjunction with the accompanying drawing. It is to be expressly understood that the drawing is for the purpose of illustration and description and is not intended as a definition of the limits of the invention. These and other objects attained, and advantages offered, by the present invention will become more fully apparent as the description that now follows is read in conjunction with the accompanying drawing.